Painting of a molded urethane part

ABSTRACT

Molded urethane automobile parts containing an internal waxy mold release agent that normally causes &#39;&#39;&#39;&#39;fisheying&#39;&#39;&#39;&#39; in urethane paints used to topcoat such parts are effectively painted by first applying a thin clear coat of the thermosetting vehicle of a urethane-type paint free of pigment, at least partially curing the clear coating to bind the lubricant or mold release agent, followed by application of the pigmented final color coat of a urethane paint and fully curing both coats.

United States Patent 1191 McDowell et al. Oct. 7, 1975 [5 1 PAINTING OFA MOLDED URETHANE 3,516,957 6/1970 Gray et a1. 264/300 x PART 3,639,1472/1972 Benefiel et a1. 1 17/72 X 3,698,927 10/1972 Sawyer ll7/l38.8 D X[75] Inventors: Floyd E. McDowell, Exeter; Michael 3 752,695 8/1973 Fin1|i 117/138 8 D X J. Williams, Somersworth, both of 3,817,774 6/1974Kuzmik 117/47 A N.l-l.

[73] Assignee: McCord Corporation, Detroit, Primary ExaminerRalph HusackMich Attorney, Agent, or FirmMcGlynn and Milton [22] Filed: Feb. 19,1974 21 App]. No.: 443,319

[52] US. Cl. 427/316; 427/307; 427/322; 427/379; 427/385; 427/407;428/425 [51] Int. C1. B32B 27/40; BOSD 1/38 [58] Field of Search 117/72,138.8 D, 47 A, 117/47 l-l; 161/190; 264/300, DIG. 77; 427/316, 307, 322,379, 385, 407

[56] References Cited UNITED STATES PATENTS 3,442,837 5/1969 Brotz etal. 264/300 X Molded urethane automobile parts containing an internalwaxy mold release agent that normally causes fisheying in urethanepaints used to topcoat such parts are effectively painted by firstapplying a thin clear coat of the thermosetting vehicle of aurethanetype paint free of pigment, at least partially curing the clearcoating to bind the lubricant or mold release agent, followed byapplication of the pigmented final color coat of a urethane paint andfully curing both coats.

ABSTRACT 4 Claims, 1 Drawing Figure Mold Urethane Part with InternalMold Release Agent Apply CI of Urethane Vehicle ear Coat l2 1 PartiallyCure ClearCoat I Apply Color Coat of Vehicle Pl us Pigment Fully CureBoth Films Mold Urerhane Parr IO with Internal Mold W Release Agent llClean Surface Apply Clear Coal l2 of Urethane Vehicle l Partially CureClear Coal Apply Color Coal of 4 Vehicle Plus Pigment ll Fully Cure BolhFilms flw 1 x PAINTING OF A MOLDED URETI-IANE PART INTRODUCTION Certainautomobile interior and exterior parts are now made from moldedurethanes such as the so-called thermoplastic urethanes and theself-skinning urethane foams. Such parts after molding are painted tocolor match the color of the automobile.

Internal mold release agents are customarily used in the manufacture ofsuch parts, such as waxes added to the molding formulations whichmigrate, bleed or bloom to the surface during molding and aid in releaseof the part during demolding. When a paint comprising a vehicle and apigment is applied to such a molded surface the mold release agent canbe absorbed by the paint film and effect the forces that hold thepigment in dispersion in the paint such that fisheying or crawling willoccur in the paint film, i.e., the pigment in the paint tends toseparate in areas where the mold release agent or lubricant is presenton the surface of the part such that pigment pockets or voids result.

The mold release agents that are preferred are usually esters or amidesof C C fatty acids. Once they have migrated to the surface and servedtheir mold release function, they are quite difficult to remove.Reasonably cleaning with solvents or detergents will often not reliablydo so.

THIS INVENTION It has now been found that when such molded parts are tobe painted with a urethane type paint that contains a dispersed pigment,the deleterious effect of the mold release agent on the surface can beblocked by first applying a clear coat of only the urethane vehicle ofthe paint and at least partially heat curing the clear coat followingwhich the part can be painted in the normal manner. It has been foundthat the lubricant on the surface of the part does not prevent wettingand uniform film formation by the urethane vehicle and that once theclear film is at least partially cured this seems to lock the lubricantin and prevent further migration of any significant amount thereof thatwould be harmful to the subsequently applied paint film.

In one situation where Chevrolet 8" and Cadillac bumper end fillers werebeing manufactured, rejects because of unsatisfactory paint filmformation were reduced from an average of 10 to 12 per cent to under 3per cent by the use of the barrier coat technique of this invention.

Full curing of the clear barrier coat prior to the application of thefinal topcoat does not appear to be required. Heating of the film to atrue film temperature in a range of 180 to 260F appears to adequatelybind the lubricant while leaving the barrier coat film sufficientlyuncured to bind well with the topcoat when it is applied. The barrierwhen partially cured in this manner will not normally pass the xylenerubbing test although in some cases it may be sufficiently cured to doso. Too hard a cure of the clear barrier coat may prevent the topcoatfrom effectively bonding with it. After the topcoat is applied bothfilms are fully cured by heating them to a temperature above 225F.

The clear barrier coat film while continuous need not have a thicknessof greater than 0.5 mil as film thick nesses in the order of 0.2 to 0.4mil seems to lock adequately the mold release lubricant in againstmigration. Thicker films may contribute to cold flex cracking. The

top pigment-containing paint film can have the customary thickness,usually about one mil or more.

Generally it is desirable to remove as much as possible of the moldrelease agent by solvent degreasing, detergent washing or the like so asto minimize the chance of strike through.

Because both the barrier coat and the paint contain a solvent, it ispreferred to heat the part to a temperature greater than 130F prior totheir application and to allow the part to air flash after theapplication of the barrier coat and after the application of the paint.

While the paints used in the present inventions are referred to asurethane paints or urethane lacquers, they are more properly identifiedas urethanepolyester-extended melamine lacquers the vehicles of whichare cross-linkable or heatcurable.

DRAWING Attached to and forming a part hereof is a drawing whichschematically illustrates the significant steps of the process of thisinvention and is self-explanatory.

In the drawing the first block, block 10, is labeled Mold Urethane Partwith Internal Mold Release Agent. Block 11 is labeled Clean Surface andblock 12 is labeled Apply Clear Coat of Urethane Vehicle. Block 13 islabeled Partially Cure Clear Coat." Block 14 is labeled Apply Color Coatof Vehicle Plus Pigment and block 15 is labeled Fully Cure Both Films.

EXAMPLE Test blocks 8 inches X 8 inches X Aa inch are prepared byinjection molding of a thermoplastic urethane, Roylar E-2B sold byUniroyal Chemical, Naugatuck, Connecticut, 60770, to which 0.3 weightpercent of ethylene-bis-stearamide is added as a mold release agent.Advawax 280 F sold by Cincinnati Milacron Chemicals, Inc. Reading, Ohio45215 could as well be used. The surface of the test blocks are cleanedby washing with a xylene soaked rag.

The clear lacquer used is Durathane applied by an air gun as supplied bythe manufacture, Pittsburgh Plate and Glass Chemical Company. The colorcoat used is Durathane lOO dark metallic green (WV-4517) also applied byair gun as supplied.

The test blocks are preheated to F prior to application of the firstcoat and are allowed to air flash for about 5 minutes after the firstcoat is applied.

One block is coated with the color coat after the solvent washing andafter the air flash it may be noticed that unacceptable fisheying hasoccurred.

The 8 inch X 8 inch surface of another preheated block is first coatedwith a 0.3 mil film (dry) of the clear Durathane 100, air flashed andbaked 30 minutes at 200F. After allowing some cooling but while the partis still warm the surface is sprayed with a one mil film (dry) of thecolor coat, air flashed for a few minutes then baked at 240F for 30minutes. Paint film formation will be noticed to be good and the samplewill pass all of the usual tests such as flex cracking, aging,weathering, and the like.

We claim:

1. In the painting with a paint of a molded urethane part made from amoldable urethane formulation containing a wax of a type and in anamount sufficient to serve as a mold release agent, said paintcomprising a urethane lacquer vehicle with a pigment dispersed therein,the improvement comprising:

A. cleaning a surface of said part to at least in part remove said waxtherefrom:

B. applying a clear continuous barrier coat to said surface of saidvehicle free of pigment as a film having a thickness under 0.5 mil, dry;

C. at least partially curing said barrier coat by heating to a filmtemperature in the range of l80260F, and

D. applying said paint as a film and curing said film by baking at afilm temperature in excess of 225F.

2. The process of claim 1 wherein said barrier coat lene-bis-stearamide.

1. IN THE PAINTING WITH A PAINT OF A MOLDED URETHANE PART MADE FROM AMOLDABLE URETHANE FORMULATION CONTAINING A WAX OF A TYPE AND IN ANAMOUNT SUFFICIENT TO SERVE AS A MOLD RELEASE AGENT, SAID PAINTCOMPRISING A URETHANE LACQUER VEHICLE WITH A PIGMENT DISPERSED THEREIN,THE IMPROVEMENT COMPRISING: A. CLEANING A SURFACE OF SAID PART TO ATLEAST IN PART REMOVE SAID WAX THEREFROM: B. APPLYING A CLEAR CONTINUOUSBARRIER COAT TO SAID SURFACE OF SAID VEHICLE FREE OF PIGMENT AS A FLIMHAVING A THICKNESS UNDER 0.5 MIL, DRY, C. AT LEAST PARTIALLY CURING SAIDBARRIER COAT BY HEATING TO A FLIM TEMPERATURE IN THE RANGE OF180*-260*F, AND D. APPLYING SAID PAINT AS A FLIM AND CURING SAID FLIM BYBAKING AT A FILM TEMPERATURE IN EXCESS OF 225*F.
 2. The process of claim1 wherein said barrier coat and said paint contain a solvent and areapplied to said part after the part has been heated to a temperaturegreater than 130*F, and the part is allowed to air flash afterapplication of the barrier coat, and after application of said paintprior to baking.
 3. The process of claim 1 wherein said wax is selectedfrom the group consisting of esters and amides of c12-C24 fatty acidsand said film of said paint has a thickness of at least 1 mil, dry. 4.The process of claim 1 wherein said wax is ethylene-bis-stearamide.